Process and methods of purification for the manufacture fluorocarbons

ABSTRACT

Halocarbons of the structure CF 3 CF 2 CH 2 X, wherein X is either F or Cl or mixtures thereof prepared by: contacting at least one 2-fluorochloropropane with hydrogen fluoride in a first fluorination step in the gas phase or liquid phase under substantially anhydrous conditions, in the absence of added catalyst to partially fluorinate said 2-fluorochloropropane; contacting said partially fluorinated 2-fluorochloropropane with at least the stoichiometric molar equivalent of hydrogen fluoride under substantially anhydrous conditions, in the presence of at least one fluorination catalyst in a second fluorination step; removing said reaction products from contact with said catalyst, and isolating a substantial yield of at least 1,1,1,2,2,3-hexafluoropropane or 1,1,1,2,2,penta-3-chloropropane, or mixtures thereof, respectively.

CROSS REFERENCE(S) TO RELATED APPLICATION(S)

This application claims the benefit of priority of U.S. ProvisionalApplication 60/842,550, filed Sep. 5, 2006.

BACKGROUND INFORMATION

1. Field of the Disclosure

This disclosure relates in general to the preparation of halocarbons3-chloro-1,1,1,2,2-pentafluoropropane (HCFC-235cb) and1,1,1,2,2,3-hexafluoropropane (HFC-236cb), and azeotropic andnear-azeotropic compositions comprising the fluorocarbons and hydrogenfluoride.

2. Description of the Related Art

The refrigeration industry has been working for the past few decades tofind replacement refrigerants for the ozone depletingchlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) beingphased out as a result of the Montreal Protocol. The solution for mostrefrigerant producers has been the commercialization ofhydrofluorocarbon (HFC) refrigerants. HFCs, however, are now beingregulated due to concerns related to global warming.

There is always a need for new and better processes for the preparationof halocarbons that may be useful as refrigerants or in otherapplications such as foam expansion agents, aerosol propellants, firesuppression or extinguishing agents, solvents, and sterilants to name afew.

DESCRIPTION

Described is a composition comprising a halocarbon of the structureCF₃CF₂CH₂X, wherein X is either F or Cl or mixtures thereof prepared by:

contacting at least one 2-fluorochloropropane with hydrogen fluoride ina first fluorination step in the gas phase or liquid phase undersubstantially anhydrous conditions, in the absence of added catalyst topartially fluorinate said 2-fluorochloropropane;

contacting said partially fluorinated 2-fluorochloropropane with atleast the stoichiometric molar equivalent of hydrogen fluoride undersubstantially anhydrous conditions, in the presence of at least onefluorination catalyst in a second fluorination step;

removing said reaction products from contact with said catalyst andisolating a substantial yield of at least 1,1,1,2,2,3-hexafluoropropaneor 1,1,1,2,2,penta-3-chloropropane or mixtures thereof, respectively.

The process may further include the step after separating CF₃CF₂CH₂Xcompounds and hydrogen fluoride (HF) from other components in thereaction product mixture (after the reaction products are removed fromthe catalyst by subjecting said reaction product mixture to adistillation step forming a column distillate composition comprising anazeotropic or near-azeotropic composition of said CF₃CF₂CH₂X andhydrogen fluoride (HF) essentially free of chlorofluorocarbons.

Also described is a process for the preparation of halocarbons of theformula CF₃CF₂CH₂X, wherein X is either F or Cl or mixtures thereof,comprising contacting at least one 2-fluorochloropropane with hydrogenfluoride in a first fluorination step, in one embodiment, in the gasphase or in another embodiment, in the liquid phase under in anotherembodiment, substantially anhydrous conditions in the absence of addedcatalyst to partially fluorinate the 2-fluorochloropropane, followed bycontacting the partially fluorinated 2-fluorochloropropane with at leastthe stoichiometric molar equivalent of hydrogen fluoride undersubstantially anhydrous conditions in a second fluorination step, in thepresence of a fluorination catalyst, and removing the reaction productsfrom the catalyst and separating said CF₃CF₂CH₂X from otherfluorochlorocarbons by forming a mixture of said CF₃CF₂CH₂X, otherfluorochlorocarbons and hydrogen fluoride and subjecting said mixture toa distillation step forming a column distillate composition comprisingan azeotropic or near-azeotropic composition of said CF₃CF₂CH₂X andhydrogen fluoride essentially free of chlorofluorocarbons.

Further described are azeotropic or near-azeotropic compositions1,1,1,2,2,3-hexafluoropropane and hydrogen fluoride and1,1,1,2,2-pentafluoro-3-chloropropane and hydrogen fluoride.

Further described is a process for the separation of1,1,1,2,2,3-hexafluoropropane from a mixture comprising an azeotropic ornear-azeotropic composition of 1,1,1,2,2,3-hexafluoropropane andhydrogen fluoride, said process comprising:

-   -   (a) Subjecting said mixture to a first distillation step in        which a composition enriched in either (i) hydrogen fluoride        or (ii) 1,1,1,2,2,3-hexafluoropropane is removed as a first        distillate composition with a first bottoms composition being        enriched in the other of said components (i) or (ii); and    -   (b) Subjecting said first distillate composition to a second        distillation step conducted at a different pressure that the        first distillation step in which the component enriched as a        first bottoms composition in (a) is removed in a second        distillate with a second bottoms composition enriched in the        same component which was enriched in the first distillate        composition.

Optionally, a first distillation step is carried out at a pressure thatis greater than the second distillation step.

Further described is a process for the separation of1,1,1,2,2-pentafluoro-3-chloropropane from a mixture comprising anazeotropic or near-azeotropic composition of1,1,1,2,2-pentafluoro-3-chloropropane and hydrogen fluoride, saidprocess comprising:

-   -   a) subjecting said mixture to a first distillation step in which        a composition enriched in either (i) hydrogen fluoride or (ii)        1,1,1,2,2-pentafluoro-3-chloropropane is removed as a first        distillate composition with a first bottoms composition being        enriched in the other of said components (i) or (ii); and    -   b) subjecting said first distillate composition to a second        distillation step conducted at a different pressure than the        first distillation step in which the component enriched as first        bottoms composition in (a) is removed in a second distillate        composition with a second bottoms composition enriched in the        same component which was enriched in the first distillate        composition.

Optionally, the second distillation step is carried out at a pressuregreater than the pressure of the first distillation step.

The foregoing general description and the following detailed descriptionare exemplary and explanatory only and are not restrictive of theinvention, as defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated in the accompanying figures to improveunderstanding of concepts as presented herein.

FIG. 1 is a schematic illustrating some embodiments of the process formaking 3-chloro-1,1,1,2,2-pentafluoropropane (HCFC-235cb) or1,1,1,2,2,3-hexafluoropropane (HFC-236cb).

FIG. 2 is a schematic illustrating a two column pressure swingdistillation process for separating3-chloro-1,1,1,2,2-pentafluoropropane (HCFC-235cb) or1,1,1,2,2,3-hexafluoropropane (HFC-236cb) from HF.

Skilled artisans appreciate that objects in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.For example, the dimensions of some of the objects in the figures may beexaggerated relative to other objects to help to improve understandingof embodiments.

As used herein, the term 2-fluorochloropropane refers to compounds ofthe formula CCl₃CYFCH₂Cl, wherein Y is F or Cl. Hence2-fluorochloropropane refers to either2-fluoro-1,1,1,2,3-pentachloropropane (HCFC-231 bb), or to2,2-difluoro-1,1,1,3-tetrachloropropane (HCFC-232cb). As used herein,partially fluorinate means to replace one, two, or three chlorine atomsof the CCl₃ group of the 2-fluorochloropropane with fluorine atoms toincrease the fluorine content of the halogenated hydrocarbon, or toproduce a mixture of such partially fluorinated 2-fluorochloropropanes.The degree of fluorination reflects the number of fluorine substituentsthat replace chlorine substituents in the CCl3CYIFCH2Cl startingmaterial and its converted products. For example, CF3CF2CH2Cl(HCFC-235cb) represents a higher degree of fluorination thanCCl3CClFCH2Cl (HCFC-231bb)

As used herein, a fluorination catalyst is a catalyst which promotes thereaction whereby a fluorine atom is substituted for a chlorine atom in ahalogenated hydrocarbon.

In one embodiment, the process is one to manufacture3-chloro-1,1,1,2,2-pentafluoropropane (HCFC-235cb), an intermediate thatmay be converted into E- and Z-1,2,3,3,3-pentafluoro-1-propene(HFC-1225ye), a pentafluoropropene isomer of high interest as a low GWPrefrigerant composition. HCFC-235cb may also be converted into2,3,3,3-tetrafluoro-1-propene (HFC-1234yf), also of interest as a lowGWP refrigerant.

In another embodiment, the process described is one to manufacture1,1,1,2,2,3-hexafluoropropane (HFC-236cb), an intermediate readilyconverted into E- and Z-1,2,3,3,3-pentafluoro-1-propene (HFC-1225ye), apentafluoropropene isomer of high interest as a low GWP refrigerantcomposition.

In one embodiment, 2-fluorochloropropanes such as1,1,1,2,3-pentachloro-2-fluoropropane are fluorinated by reaction withHF in the reaction process set forth below:CH₂Cl—CClF—CCl₃+HF→CH₂Cl—CClF—CCl₂F

-   -   Halogen Exchange        CH₂Cl—CClF—CCl₂F+HF→CH₂Cl—CClF—CClF₂    -   Halogen Exchange        CH₂Cl—CClF—CClF₂+HF→CH₂Cl—CClF—CF₃    -   Halogen Exchange        CH₂Cl—CClF—CF₃+HF→CH₂Cl—CF₂—CF₃    -   Halogen Exchange        CH₂Cl—CF₂—CF₃+HF→CH₂F—CF₂—CF₃    -   Halogen Exchange

Replacing multiple chlorine substituents in a 2-fluorochloropropane suchas CCl₃CClFCH₂Cl (HCFC-231 bb) with fluorine to produce HFC-236cb in acatalytic reactor can cause heat management problems. In someembodiments there is low equilibrium constant in the conversion ofHCFC-235cb to HFC-236cb (see equation (1)).CF₃CF₂CH₂Cl+HF

CF₃CF₂CH₂F+HCl  (1)

In some embodiments, in low equilibrium constant conversions, partiallyfluorinating a halogenated hydrocarbon precursor of the formulaCCl₃CYFCH₂Cl, in a first step and completing the fluorination in asecond, catalytic liquid phase fluorination is expected to reduce anyinherent problems. In addition, in some embodiments, partiallyfluorinating CCl₃CYFCH₂Cl, to a mixture of intermediate halogenatedhydrocarbons having a higher fluorine content gives a product that isthermally more stable than the pure CCl₃CYFCH₂Cl, with respect to tarformation. In addition, in some embodiments, by reducing the number ofchlorine atoms to be exchanged in the second fluorination step thelimitations introduced by the equilibrium in equation (1) are reduced.

The degree to which halogen exchange reactions proceed can be varied byvarying the amount of HF and catalyst in combination as described hereinbelow. In some embodiments, the halogen exchange reaction may becomprised of a first fluorination step wherein thepentachlorofluoropropane is contacted with HF in the absence of addedcatalyst, followed by a second fluorination step in the presence of acatalyst.

In some embodiments, the first fluorination step, starting2-fluorochloropropane is contacted with HF in the gas phase or in theliquid phase at elevated temperature. In some embodiments, the firstfluorination step is conducted in the liquid phase, heating a mixture ofHF and 1,1,1,2,3-pentachloro-2-fluoropropane from room temperature tofrom about 100° C. to about 150° C. In some embodiments, the firstfluorination time can be from about 15 minutes to about 4 hours. In someembodiments, the amount of HF relative to the amount of2-fluorochloropropane may be from about 5 moles to about 50 moles of HFper mole of 2-fluorochloropropane. In other embodiments, the amount ofHF relative to the amount of 2-fluorochloropropane may be from about 10moles to about 30 moles of HF per mole of 2-fluorochloropropane. In someembodiments, hydrogen chloride is removed after the first fluorinationstep, prior to the second fluorination step.

The products of fluorination of 2-fluorochloropropane with HF may beused directly in the next step of the process or may be subjected to oneof several purification schemes. In some embodiments, the reaction iscarried out in such a way that the HCl produced during the fluorinationof a 2-fluorochloropropane is removed via a distillation column presentin the system. The same or a different distillation column may removereaction products having the desired degree of fluorination from thereactor leaving unconverted 2-fluorochloropropane or products having alower degree of fluorination in the reactor for further reaction. Thefluorinated products removed from the reactor are then sent to avaporizer or heated zone where they are brought to the desiredtemperature of the second step of the fluorination process.Alternatively, the entire reaction effluent formed by contacting a2-fluorochloropropane with HF in the first reaction zone may be sent toa vaporizer or heated zone and then to the second fluorination stepoptionally with the further addition of HF.

In some embodiments, the second fluorination step is carried out in theliquid phase in the presence of a fluorination catalyst. In someembodiments, the second fluorination step is carried out in the vaporphase in the presence of a fluorination catalyst. In some embodiments,the fluorination catalyst is at least one selected from the groupconsisting of: AlF₃, BF₃, FeX₃, where X is the same or different and isselected from the group consisting of Cl and F, SbCl_(3-x)F_(x) (x=0 to3), AsF₃, MCl_(5-y)F_(y) (wherein M is one of Sb, Nb, Ta or Mo, and y=0to 5), M′Cl_(4-z)F_(z) (wherein M′ is one of Sn, Ti, Zr, Hf, and z=0 to4), or mixtures thereof. In other embodiments, the fluorination catalystis MCl_(5-y)F_(y) (wherein M is one of Sb, Nb, Ta, and y=0 to 5) ormixtures thereof. Highly fluorinated catalysts such as for example, MF₅when M=Nb or Ta and SbCl_(k)F_(5-k) where k=0 to 3 may be convenientlyprepared by fluorination of the chlorinated precursors, MCl₅ or SbCl₅,or SbCl₃+Cl₂, with HF either in the second fluorination reactor or in aseparate fluorination step. In some embodiments, the FeX₃ is supportedon carbon. In other embodiments, two or more fluorination catalyst canbe used in the second fluorination step.

In some embodiments, to achieve the maximum degree of halogen exchange,at least 0.05 molar equivalent fluorination catalyst, based on thestarting 2-fluorochloropropane is required. In other embodiments, toachieve the maximum degree of halogen exchange at least about 0.25 molarequivalents to about 5.0 molar equivalents of fluorination catalyst,based on the starting 2-fluorochloropropane is required. In yet otherembodiments, a range of catalyst is from about 0.27 molar equivalents toabout 4.0 molar equivalents.

In some embodiments, in the second fluorination step, total of thenumber of moles of HF added plus the total number of moles of availablefluorine from the catalyst must be at least equal to 5. In anotherembodiment, the molar ratio of HF to the partially fluorinatedpentachlorofluoropropane is from about 5 to about 50.

In some embodiments, the metal pentafluoride (prepared from, forexample, Ta and Nb pentachlorides) can be prepared for use in someembodiments just prior to initiating the HF-2-fluorochloropropanereaction for the preparation of the desired polyfluorinated organicproduct.

Anhydrous or substantially anhydrous conditions means that water, whichis detrimental to the reaction, should be excluded as much as possiblefrom the reaction zone. The HF which is commercially available can beused in the reaction directly. Exclusion of moisture from the reactionvessel by means of appropriate moisture traps, inert gas purging, etc.,is a routine procedure and is well known in the art.

In some embodiments, the second fluorination step can be carried out ina batchwise manner in the liquid phase at from about 0° C. to about 175°C. In another embodiment, the second fluorination step is carried out atfrom about 60° C. to about 160° C. At reaction temperatures below theselimits the reactions become too slow to be useful, and at temperatureabove these limits the yields of products are lowered by side reactionsand polymerization. In yet other embodiments, the second fluorinationstep in carried out in a continuous manner.

The reaction vessel is constructed from materials which are resistant tothe action of hydrogen fluoride. Examples include stainless steels, highnickel alloys such as monel, “Hastelloy” and “Inconel”, and plasticssuch as polyethylene, polypropylene, polychlorotrifluoroethylene andpolytetrafluoroethylene. The high nickel alloys are preferred because ofthe superacidities of some fluorination catalysts in combination withliquid HF. For reactions at a temperature either below the boiling pointof hydrogen fluoride (19.5° C.) or below the boiling point of the mostvolatile reactant, the reaction vessel can be closed or open to theatmosphere if provisions to exclude moisture are taken. For reactions ata temperature at or above the boiling point of hydrogen fluoride or themost volatile component, a closed vessel or a pressure-regulatedpartially open reaction is used to minimize the loss of the reactants.

In some embodiments, pressure is not critical. In other embodiments, theprocess is preformed at atmospheric and autogenous pressures. Means canbe provided for the venting of the excess pressure of hydrogen chlorideformed in the substitution reaction and can offer an advantage inminimizing the formation of side products.

In some embodiments, the reactions are conducted by introducing thereagent in any order into the reaction vessel. The first fluorinationstep may be conducted first in one reaction vessel, and then thecontents transferred to a second vessel with catalyst. In otherembodiments, the first fluorination and the catalyzed fluorination stepcan be conducted in the same reaction vessel. In other embodiments, inbatch-type autogenous pressure operation, the catalyst and startingmaterial are placed in the reaction vessel which is then cooled, and therequired amount of hydrogen fluoride is condensed in the vessel. Thevessel may be cooled in dry Ice or liquid nitrogen and evacuated priorto the introduction of hydrogen fluoride to facilitate the hydrogenfluoride addition. The contents of the vessel are raised to theappropriate reaction temperature and agitated by shaking or stirring fora length of time sufficient to cause the reaction to occur. The reactiontimes can be from about 1 to about 17 hours. In other embodiments, thereaction times may be from about 1 to about 6 hours.

In other embodiments, the fluorination reaction can be conducted in acontinuous or semi-continuous manner with HF and the halocarbon startingmaterial fed continuously or intermittently to a first reaction vessel,and from there to a second reaction vessel containing the fluorinationcatalyst at a temperature and pressure effective to result in thefluorination of the starting material to the desired polyfluorinatedproduct. In other embodiments, the temperature and pressure are suchthat the desired product is in the gaseous state, so that a reactionproduct stream can be removed continuously or intermittently from thereaction zone. In other embodiments, the pressure within the reactor canbe controlled by means of a pressure regulator, and the temperature ofthe reaction product stream can be controlled, if desired, by use of acondenser/dephlegmator, all these techniques being well known to theart.

In some embodiments, the reaction of HF with partially fluorinated2-fluorochloropropane in the presence of at least one fluorinationcatalyst and can be conducted in the presence of a diluent which may bea high boiling inert liquid, e.g., a perfluorinated hydrocarbon, or thedesired reaction product itself, CF₃CF₂CH₂X, wherein X═F or Cl.

In some embodiments, for the preparation of1,1,1,2,2,3-hexafluoropropane, and the isolation of1,1,1,2,2,3-hexafluoropropane, the 1,1,1,2,2,3-hexafluoropropane formsan azeotrope with HF.

In some embodiments, provided is a composition, which comprises1,1,1,2,2,3-hexafluoropropane and an effective amount of hydrogenfluoride (HF) to form an azeotropic composition. By effective amount ismeant an amount, which, when combined with1,1,1,2,2,3-hexafluoropropane, results in the formation of an azeotropicor near-azeotropic mixture.

Compositions may be formed that comprise azeotropic combinations ofhydrogen fluoride with 1,1,1,2,2,3-hexafluoropropane. In someembodiments, these include compositions comprising from about 36.9 molepercent to about 55.1 mole percent HF and from about 63.1 mole percentto about 44.9 mole percent 1,1,1,2,2,3-hexafluoropropane (which forms anazeotrope boiling at a temperature from between about −6.1° C. and about108° C. and at a pressure from between about 15 psi and about 490 psia).

In other embodiments, near-azeotropic compositions containing HF and1,1,1,2,2,3-hexafluoropropane may also be formed. Such near-azeotropiccompositions comprise about 38 mole percent to about 75.8 mole percent1,1,1,2,2,3-hexafluoropropane and about 24.2 mole percent to about 62mole percent HF at temperatures ranging from about −20° C. to about 120°C. and at pressures from about 8 psi to about 389 psi.

In other embodiments, compositions may be formed that consistessentially of azeotropic combinations of hydrogen fluoride with1,1,1,2,2,3-hexafluoropropane. These include compositions consistingessentially of from about 36.9 mole percent to about 55.1 mole percentHF and from about 63.1 mole percent to about 44.9 mole percent1,1,1,2,2,3-hexafluoropropane (which forms an azeotrope boiling at atemperature from between about −6.1° C. and about 108° C. and at apressure from between about 15 psi and about 490 psi.

In other embodiments, near azeotropic compositions may also be formedthat consist essentially of about 38 mole percent to about 75.8 molepercent 1,1,1,2,2,3-hexafluoropropane and about 24.2 mole percent toabout 62 mole percent HF at temperatures ranging from about −20° C. toabout 120° C. and at pressures from about 8 psi to about 389 psi.

In considering a process for the preparation of1,1,1,2,2-pentafluoro-3-chloropropane, and the isolation of1,1,1,2,2-pentafluoro-3-chloropropane from such a process, it has beendiscovered surprisingly that the 1,1,1,2,2-pentafluoro-3-chloropropaneforms an azeotrope with HF.

In some embodiments, provided is a composition, which comprises1,1,1,2,2-pentafluoro-3-chloropropane and an effective amount ofhydrogen fluoride (HF) to form an azeotropic composition. By effectiveamount is meant an amount, which, when combined with1,1,1,2,2-pentafluoro-3-chloropropane, results in the formation of anazeotropic or near-azeotropic mixture.

Compositions may be formed that comprise azeotropic combinations ofhydrogen fluoride with 1,1,1,2,2-pentafluoro-3-chloropropane. In someembodiments, these include compositions comprise from about 65.1 molepercent to about 82.7 mole percent HF and from about 34.9 mole percentto about 17.3 mole percent 1,1,1,2,2-pentafluoro-3-chloropropane (whichforms an azeotrope boiling at a temperature from between about 8.2° C.and about 127.1° C. and at a pressure from between about 15 psi andabout 480 psi.

In other embodiments, near-azeotropic compositions containing HF1,1,1,2,2-pentafluoro-3-chloropropane may also be formed. Suchnear-azeotropic compositions comprise about 11.4 mole percent to about38.8 mole percent 1,1,1,2,2-pentafluoro-3-chloropropane and about 61.2mole percent to about 88.6 mole percent HF at temperatures ranging fromabout −20° C. to about 120° C. and at pressures from about 4.2 psi toabout 245.6 psi.

It should be understood that while an azeotropic or near-azeotropiccomposition may exist at a particular ratio of the components at giventemperatures and pressures, the azeotropic composition may also exist incompositions containing other components. These additional componentsinclude the individual components of the azeotropic composition, saidcomponents being present as an excess above the amount being present asthe azeotropic composition. For instance, the azeotrope of1,1,1,2,2-pentafluoro-3-chloropropane and HF may be present in acomposition that has an excess of 1,1,1,2,2-pentafluoro-3-chloropropane,meaning that the azeotropic composition is present and additional1,1,1,2,2-pentafluoro-3-chloropropane is also present.

In other embodiments, compositions may be formed that consistessentially of azeotropic combinations of hydrogen fluoride with1,1,1,2,2-pentafluoro-3-chloropropane. These include compositionsconsisting essentially of from about 65.1 mole percent to about 82.7mole percent HF and from about 17.3 mole percent to about 34.9 molepercent 1,1,1,2,2-pentafluoro-3-chloropropane (which forms an azeotropeboiling at a temperature from between about 8.2° C. and about 127.1° C.and at a pressure from between about 15 psi and about 480 psi).

In yet other embodiments, near azeotropic compositions may also beformed that consist essentially of about 11.4 mole percent to about 38.8mole percent 1,1,1,2,2-pentafluoro-3-chloropropane and about 61.2 molepercent to about 88.6 mole percent HF at temperatures ranging from about−20° C. to about 120° C. and at pressures from about 4.2 psi to about245.6 psi.

At atmospheric pressure, the boiling points of hydrofluoric acid and1,1,1,2,2,3-hexafluoropropane are about 19.5° C. and about −1° C.,respectively.

In some embodiments, the HF/1,1,1,2,2,3-hexafluoropropane azeotropic andnear-azeotropic compositions are useful in processes to produce1,1,1,2,2,3-hexafluoropropane and in processes to purify1,1,1,2,2,3-hexafluoropropane The HF/1,1,1,2,2,3-hexafluoropropaneazeotropic and near-azeotropic compositions may be useful in any processthat creates a composition containing 1,1,1,2,2,3-hexafluoropropane andHF.

In some embodiments, azeotropic distillation with hydrogen fluoride maybe carried out to separate 1,1,1,2,2,3-hexafluoropropane fromHCFC-235cb. HCFC-235cb may be converted to HFC-236cb by fluorination asdisclosed herein. A two-column pressure-swing distillation may then becarried out to separate the HF from the desired1,1,1,2,2,3-hexafluoropropane product. And in other embodiments,two-column pressure-swing distillation may be carried out to separate HFfrom HCFC-235cb. HF may also be removed from the halogenated hydrocarboncomponents of the product mixture using, for example, standard aqueoussolution scrubbing techniques. However, the production of substantialamounts of scrubbing discharge can create aqueous waste disposalconcerns. Thus, there remains a need for processes recovering HF fromsuch product mixtures.

While the initial mixture treated in accordance with the processesdisclosed herein can be obtained from a variety of sources, including byadding 1,1,1,2,2,3-hexafluoropropane to HF-containing compositions, inone embodiment, an advantageous use of the disclosed processes residesin treating the effluent mixtures from the preparation of1,1,1,2,2,3-hexafluoropropane.

In some embodiments, another aspect provides a process for theseparation of 1,1,1,2,2,3-hexafluoropropane from HCFC-235cb comprising:a) forming a mixture of 1,1,1,2,2,3-hexafluoropropane, HCFC-235cb, andhydrogen fluoride; and b) subjecting said mixture to a distillation stepforming a column distillate composition comprising an azeotropic ornear-azeotropic composition of HF and 1,1,1,2,2,3-hexafluoropropaneessentially free of HCFC-235cb, as an overhead stream. In someembodiments, a bottoms stream from such a distillation comprisesHCFC-235cb. In other embodiments, a bottoms stream from such adistillation comprises HCFC-235cb and hydrogen fluoride.

Use of the term “essentially free of HCFC-235cb” means that thecomposition contains less than about 100 ppm HCFC-235cb (on a molebasis). In other embodiments, “essentially free of HCFC-235cb” meansthat the composition contains less than about 10 ppm HCFC-235cb (molebasis). In yet other embodiments, “essentially free of HCFC-235cb” meansthat the composition contains less than about 1 ppm, of HCFC-235cb (molebasis).

This azeotropic/near azeotropic distillation takes advantage of the lowboiling azeotropic and near azeotropic compositions formed by1,1,1,2,2,3-hexafluoropropane and HF. The azeotropic composition boilsat a temperature lower than the boiling point of either pure componentand lower than the boiling point of HCFC-235cb as well.

As stated previously, the mixture of 1,1,1,2,2,3-hexafluoropropane,HCFC-235cb and HF may be formed by any practical means. In someembodiment, the disclosed process is useful for the separation of1,1,1,2,2,3-hexafluoropropane from the reaction mixture produced by thefluorination of HCFC-231 bb. The reaction mixture produced may then betreated by the instant process to remove HCFC-235cb. The1,1,1,2,2,3-hexafluoropropane is taken overhead as the distillate fromthe distillation column as an azeotropic or near-azeotropic compositionof 1,1,1,2,2,3-hexafluoropropane with HF. The HCFC-235cb is taken out ofthe bottom of the column as a bottoms composition and may contain someamount of HF, as well. The amount of HF in the HCFC-235cb from thebottom of the distillation column may vary from about 35 mole percent toless than 1 part per million (ppm, mole basis) depending on the mannerin which the fluorination reaction is conducted. In fact, if thefluorination reaction is conducted in a manner to provide 50 percentconversion of the HCFC-235cb and the reaction mixture leaving thereaction zone is fed directly to the distillation step, the HCFC-235cbleaving the bottom of the distillation process will contain about 34mole percent HF.

In some embodiments, operating the disclosed azeotropic distillationinvolves providing an excess of 1,1,1,2,2,3-hexafluoropropane to thedistillation column. If the proper amount of1,1,1,2,2,3-hexafluoropropane is fed to the column, then all the HF maybe taken overhead as an azeotropic composition containing1,1,1,2,2,3-hexafluoropropane and HF. Thus, the HCFC-235cb removed fromthe column bottoms will be essentially free of HF.

Use of the term “essentially free of HF” means that the HF is present inan amount less than about 100 ppm HF (on a mole basis). In someembodiments, essentially free of HF means that HF is present in amountsless than 10 ppm (mole basis); and, in other embodiments, essentiallyfree of HF means that HF is present in amounts less than 1 ppm (molebasis).

In some embodiments, in the distillation step, the distillate exitingthe distillation column overhead comprising HF and1,1,1,2,2,3-hexafluoropropane may be condensed using, for example,standard reflux condensers. At least a portion of this condensed streammay be returned to the top of the column as reflux. The ratio of thecondensed material, which is returned to the top of the distillationcolumn as reflux, to the material removed as distillate is commonlyreferred to as the reflux ratio. The specific conditions which may beused for practicing the distillation step depend upon a number ofparameters, such as the diameter of the distillation column, feedpoints, and the number of separation stages in the column, among others.The operating pressure of the distillation column may range from about10 psi pressure to about 200 psi (1380 kPa), normally about 20 psi toabout 50 psi. In some embodiments, the distillation column is operatedat a pressure of about 25 psi (172 kPa) with a bottoms temperature ofabout 44° C. and a top temperature of about 6° C. Normally, increasingthe reflux ratio results in increased distillate stream purity, butgenerally the reflux ratio ranges between 1/1 to 200/1. The temperatureof the condenser, which is located adjacent to the top of the column, isnormally sufficient to substantially condense the distillate that isexiting from the top of the column, or is that temperature required toachieve the desired reflux ratio by partial condensation.

In some embodiments, the column distillate composition comprising anazeotropic or near-azeotropic composition of HF and1,1,1,2,2,3-hexafluoropropane, essentially free of HCFC-235cb, must betreated to remove the HF and provide pure 1,1,1,2,2,3-hexafluoropropaneas product. This may be accomplished, for example, by neutralization orby a second distillation process, as described herein.

In some embodiments, a further aspect provides a process for theseparation of 1,1,1,2,2,3-hexafluoropropane from a mixture comprising anazeotropic or near-azeotropic composition of1,1,1,2,2,3-hexafluoropropane and HF, said process comprising: a)subjecting said mixture to a first distillation step in which acomposition enriched in either (i) hydrogen fluoride or (ii)1,1,1,2,2,3-hexafluoropropane is removed as a first distillatecomposition with a first bottoms composition being enriched in the otherof said components (i) or (ii); and b) subjecting said first distillatecomposition to a second distillation step conducted at a differentpressure than the first distillation step in which the componentenriched in the first bottoms composition in (a) is removed in a seconddistillate composition with a second bottoms composition enriched in thesame component which was enriched in the first distillate composition.

The process as described above takes advantage of the change inazeotrope composition at different pressures to effect the separation of1,1,1,2,2,3-hexafluoropropane and HF. In one embodiment, the firstdistillation step is carried out at a higher pressure relative to thesecond distillation step. At higher pressures, theHF/1,1,1,2,2,3-hexafluoropropane azeotrope contains more1,1,1,2,2,3-hexafluoropropane, or less HF. Thus, this high-pressuredistillation step produces an excess of HF, which boiling at a highertemperature than the azeotrope will exit the column as the bottoms asessentially pure HF. The first column distillate is then fed to a seconddistillation step operating at lower pressure. At the lower pressure,the HF/1,1,1,2,2,3-hexafluoropropane azeotrope shifts to lowerconcentrations of 1,1,1,2,2,3-hexafluoropropane. Therefore, in thissecond distillation step, there exists an excess of1,1,1,2,2,3-hexafluoropropane. The excess 1,1,1,2,2,3-hexafluoropropane,having a boiling point higher than the azeotrope, exits the seconddistillation column as the bottoms composition. The disclosed processmay be conducted in such as manner as to produce1,1,1,2,2,3-hexafluoropropane essentially free of HF. Additionally, thedisclosed process may be conducted in such a manner as to produce HFessentially free of 1,1,1,2,2,3-hexafluoropropane.

In other embodiments, the first distillation step is carried out at alower pressure relative to the second distillation step. At lowerpressures, the HF/1,1,1,2,2,3-hexafluoropropane azeotrope contains less1,1,1,2,2,3-hexafluoropropane. Thus, this low-pressure distillation stepproduces an excess of 1,1,1,2,2,3-hexafluoropropane, which boiling at ahigher temperature than the azeotrope will exit the column as thebottoms as essentially pure 1,1,1,2,2,3-hexafluoropropane. The firstcolumn distillate is then fed to a second distillation step operating athigher pressure. At the higher pressure, theHF/1,1,1,2,2,3-hexafluoropropane azeotrope shifts to higherconcentrations of 1,1,1,2,2,3-hexafluoropropane, or lower concentrationsof HF. Therefore, in this second distillation step, there exists anexcess of HF. The excess HF, having a boiling point higher than theazeotrope, exits the second distillation column as the bottomscomposition. The disclosed process may be conducted in such as manner asto produce 1,1,1,2,2,3-hexafluoropropane essentially free of HF.Additionally, the disclosed process may be conducted in such a manner asto produce HF essentially free of 1,1,1,2,2,3-hexafluoropropane.

Use of the term “essentially free of 1,1,1,2,2,3-hexafluoropropane”means that the composition contains less than about 100 ppm1,1,1,2,2,3-hexafluoropropane (on a mole basis). In another embodiment,“essentially free of 1,1,1,2,2,3-hexafluoropropane” means that thecomposition contains less than about 10 ppm1,1,1,2,2,3-hexafluoropropane (mole basis). In yet other embodiments,“essentially free of 1,1,1,2,2,3-hexafluoropropane” means that thecomposition contains less than about 1 ppm, of1,1,1,2,2,3-hexafluoropropane (mole basis). In some embodiments of theprocess, the HCFC-235cb/HF mixture, or HFCF-235cb separated from theHFC-236cb/HF azeotrope is fed to a separate liquid phase fluorinationreactor to convert the HCFC-235cb to HFC-236cb.

In some embodiments, the HF/1,1,1,2,2-pentafluoro-3-choropropaneazeotropic and near-azeotropic compositions are useful in processes toproduce 1,1,1,2,2-pentafluoro-3-choropropane and in processes to purify1,1,1,2,2-pentafluoro-3-choropropane. In fact, theHF/1,1,1,2,2-pentafluoro-3-choropropane azeotropic and near-azeotropiccompositions may be useful in any process that creates a compositioncontaining 1,1,1,2,2-pentafluoro-3-choropropane and HF.

In some embodiments, azeotropic distillation with hydrogen fluoride maybe carried out to separate 1,1,1,2,2-pentafluoro-3-choropropane frompartially fluorinated 2-fluorochloropropanes. Partially fluorinated2-fluorochloropropanes may be converted to HCFC-235cb by fluorination asdisclosed herein. A two-column pressure-swing distillation may then becarried out to separate the HF from the desired1,1,1,2,2-pentafluoro-3-choropropane product. HF may also be removedfrom the halogenated hydrocarbon components of the product mixtureusing, for example, standard aqueous solution scrubbing techniques.However, the production of substantial amounts of scrubbing dischargecan create aqueous waste disposal concerns. Thus, there remains a needfor processes recovering HF from such product mixtures.

While the initial mixture treated in accordance with the processesdisclosed herein can be obtained from a variety of sources, including byadding 1,1,1,2,2-pentafluoro-3-choropropane to HF-containingcompositions, in one embodiment, an advantageous use of the disclosedprocesses resides in treating the effluent mixtures from the preparationof 1,1,1,2,2-pentafluoro-3-choropropane.

In some embodiments, another aspect provides a process for theseparation of 1,1,1,2,2-pentafluoro-3-choropropane from partiallyfluorinated 2-fluorochloropropanes comprising: a) forming a mixture of1,1,1,2,2-pentafluoro-3-choropropane, partially fluorinated2-fluorochloropropanes, and hydrogen fluoride; and b) subjecting saidmixture to a distillation step forming a column distillate compositioncomprising an azeotropic or near-azeotropic composition of HF and1,1,1,2,2-pentafluoro-3-choropropane essentially free of partiallyfluorinated 2-fluorochloropropanes, as an overhead stream. In oneembodiment, a bottoms stream from such a distillation comprisespartially fluorinated 2-fluorochloropropanes. In another embodiment, abottoms stream from such a distillation comprises partially fluorinated2-fluorochloropropanes and hydrogen fluoride.

Use of the term “essentially free of partially fluorinated2-fluorochloropropanes” means that the composition contains less thanabout 100 ppm partially fluorinated 2-fluorochloropropanes (mole basis).In other embodiments, “essentially free of partially fluorinated2-fluorochloropropanes” means that the composition contains less thanabout 10 ppm partially fluorinated 2-fluorochloropropanes (mole basis).In yet other embodiments, “essentially free of partially fluorinated2-fluorochloropropanes” means that the composition contains less thanabout 1 ppm, of partially fluorinated 2-fluorochloropropanes (molebasis).

This azeotropic distillation takes advantage of the low boilingazeotropic composition formed by 1,1,1,2,2-pentafluoro-3-choropropaneand HF. The azeotropic composition boils at a temperature lower than theboiling point of either pure component and lower than the boiling pointof partially fluorinated 2-fluorochloropropanes as well.

As stated previously, the mixture of1,1,1,2,2-pentafluoro-3-choropropane, partially fluorinated2-fluorochloropropanes and HF may be formed by any practical means. Insome embodiments, the disclosed process is particularly useful for theseparation of 1,1,1,2,2-pentafluoro-3-choropropane from the reactionmixture produced by the fluorination of HCFC-231 bb. The reactionmixture produced may then be treated by the instant process to removepartially fluorinated 2-fluorochloropropanes. The1,1,1,2,2-pentafluoro-3-choropropane is taken overhead as the distillatefrom the distillation column as an azeotropic or near-azeotropiccomposition of 1,1,1,2,2-pentafluoro-3-choropropane with HF. Thepartially fluorinated 2-fluorochloropropanes is taken out of the bottomof the column as a bottoms composition and may contain some amount ofHF, as well. The amount of HF in the partially fluorinated2-fluorochloropropanes from the bottom of the distillation column mayvary from about 35 mole percent to less than 1 part per million (ppm,mole basis) depending on the manner in which the fluorination reactionis conducted. In fact, if the fluorination reaction is conducted in amanner to provide 50 percent conversion of the partially fluorinated2-fluorochloropropanes and the reaction mixture leaving the reactionzone is fed directly to the distillation step, the partially fluorinated2-fluorochloropropanes leaving the bottom of the distillation processwill contain about 34 mole percent HF.

In some embodiments, operating the disclosed azeotropic distillationinvolves providing an excess of 1,1,1,2,2-pentafluoro-3-choropropane tothe distillation column. If the proper amount of1,1,1,2,2-pentafluoro-3-choropropane is fed to the column, then all theHF may be taken overhead as an azeotropic composition containing1,1,1,2,2-pentafluoro-3-choropropane and HF. Thus, the partiallyfluorinated 2-fluorochloropropanes removed from the column bottoms willbe essentially free of HF.

In some embodiments, in the distillation step, the distillate exitingthe distillation column overhead comprising HF and1,1,1,2,2-pentafluoro-3-choropropane may be condensed using, forexample, standard reflux condensers. At least a portion of thiscondensed stream may be returned to the top of the column as reflux. Theratio of the condensed material, which is returned to the top of thedistillation column as reflux, to the material removed as distillate iscommonly referred to as the reflux ratio. The specific conditions whichmay be used for practicing the distillation step depend upon a number ofparameters, such as the diameter of the distillation column, feedpoints, and the number of separation stages in the column, among others.The operating pressure of the distillation column may range from about10 psi pressure to about 200 psi (1380 kPa), normally about 20 psi toabout 50 psi. In one embodiment, the distillation column is operated ata pressure of about 25 psi (172 kPa) with a bottoms temperature of about44° C. and a top temperature of about 6° C. Normally, increasing thereflux ratio results in increased distillate stream purity, butgenerally the reflux ratio ranges between 1/1 to 200/1. The temperatureof the condenser, which is located adjacent to the top of the column, isnormally sufficient to substantially condense the distillate that isexiting from the top of the column, or is that temperature required toachieve the desired reflux ratio by partial condensation.

In some embodiments, the column distillate composition comprising anazeotropic or near-azeotropic composition of HF and1,1,1,2,2-pentafluoro-3-choropropane, essentially free of partiallyfluorinated 2-fluorochloropropanes, must be treated to remove the HF andprovide pure 1,1,1,2,2-pentafluoro-3-choropropane as product. This maybe accomplished, for example, by neutralization or by a seconddistillation process, as described herein.

In some embodiments, a further aspect provides a process for theseparation of 1,1,1,2,2-pentafluoro-3-choropropane from a mixturecomprising an azeotropic or near-azeotropic composition of1,1,1,2,2-pentafluoro-3-choropropane and HF, said process comprising: a)subjecting said mixture to a first distillation step in which acomposition enriched in either (i) hydrogen fluoride or (ii)1,1,1,2,2-pentafluoro-3-choropropane is removed as a first distillatecomposition with a first bottoms composition being enriched in the otherof said components (i) or (ii); and b) subjecting said first distillatecomposition to a second distillation step conducted at a differentpressure than the first distillation step in which the componentenriched in the first bottoms composition in (a) is removed in a seconddistillate composition with a second bottoms composition enriched in thesame component which was enriched in the first distillate composition.

The process as described above takes advantage of the change inazeotrope composition at different pressures to effect the separation of1,1,1,2,2-pentafluoro-3-choropropane and HF. In some embodiments, thefirst distillation step is carried out at a higher pressure relative tothe second distillation step. At higher pressures, theHF/1,1,1,2,2-pentafluoro-3-choropropane azeotrope contains more1,1,1,2,2-pentafluoro-3-choropropane, or less HF. Thus, thishigh-pressure distillation step produces an excess of HF, which boilingat a higher temperature than the azeotrope will exit the column as thebottoms as essentially pure HF. The first column distillate is then fedto a second distillation step operating at lower pressure. At the lowerpressure, the HF/1,1,1,2,2-pentafluoro-3-choropropane azeotrope shiftsto lower concentrations of 1,1,1,2,2-pentafluoro-3-choropropane.Therefore, in this second distillation step, there exists an excess of1,1,1,2,2-pentafluoro-3-choropropane. The excess1,1,1,2,2-pentafluoro-3-choropropane, having a boiling point higher thanthe azeotrope, exits the second distillation column as the bottomscomposition. The disclosed process may be conducted in such as manner asto produce 1,1,1,2,2-pentafluoro-3-choropropane essentially free of HF.Additionally, the disclosed process may be conducted in such a manner asto produce HF essentially free of 1,1,1,2,2-pentafluoro-3-choropropane.

In other embodiments, the first distillation step is carried out at alower pressure relative to the second distillation step. At lowerpressures, the HF/1,1,1,2,2-pentafluoro-3-choropropane azeotropecontains less 1,1,1,2,2-pentafluoro-3-choropropane. Thus, thislow-pressure distillation step produces an excess of1,1,1,2,2-pentafluoro-3-choropropane, which boiling at a highertemperature than the azeotrope will exit the column as the bottoms asessentially pure 1,1,1,2,2-pentafluoro-3-choropropane. The first columndistillate is then fed to a second distillation step operating at higherpressure. At the higher pressure, theHF/1,1,1,2,2-pentafluoro-3-choropropane azeotrope shifts to higherconcentrations of 1,1,1,2,2-pentafluoro-3-choropropane, or lowerconcentrations of HF. Therefore, in this second distillation step, thereexists an excess of HF. The excess HF, having a boiling point higherthan the azeotrope, exits the second distillation column as the bottomscomposition. The disclosed process may be conducted in such as manner asto produce 1,1,1,2,2-pentafluoro-3-choropropane essentially free of HF.Additionally, the disclosed process may be conducted in such a manner asto produce HF essentially free of 1,1,1,2,2-pentafluoro-3-choropropane.

Use of the term “essentially free of1,1,1,2,2-pentafluoro-3-choropropane” means that the compositioncontains less than about 100 ppm 1,1,1,2,2-pentafluoro-3-choropropane(mole basis). In other embodiments, “essentially free of1,1,1,2,2-pentafluoro-3-choropropane” means that the compositioncontains less than about 10 ppm 1,1,1,2,2-pentafluoro-3-choropropane(mole basis). In yet other embodiments, “essentially free of1,1,1,2,2-pentafluoro-3-choropropane” means that the compositioncontains less than about 1 ppmof 1,1,1,2,2-pentafluoro-3-choropropane(on a mole basis). In some embodiments of the process, the partiallyfluorinated 2-fluorochloropropanes/HF mixture, or HFCF-235cb separatedfrom the HCFC-235cb/HF azeotrope is fed to a separate liquid phasefluorination reactor to convert the partially fluorinated2-fluorochloropropanes to HCFC-235cb.

The preparation of 1,1,1,2,3-pentachloro-2-fluoropropane (HCFC-231 bb)from 1,2-dichloro-2-fluoropropane (HCFC-261ba) is disclosed by Henne inthe Journal of the American Chemical Society volume 63, 2692-2694, 1941,the disclosure of which is herein incorporated by reference.

The preparation of 1,1,1,3-tetrachloro-2,2-difluoropropane (HCFC-232cb)from 2,2-difluoropropane (HFC-272ca) is disclosed by Henne in theJournal of the American Chemical Society volume 59, 2434-2436, 1937, thedisclosure of which is herein incorporated by reference.

DETAILED DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic illustrating one method making3-chloro-1,1,1,2,2-pentafluoropropane (HCFC-235cb) or1,1,1,2,2,3-hexafluoropropane (HFC-236cb).

Stream 420 (may be 1,1,1,2,3-pentachloro-2-fluoropropane (HCFC-231 bb),is fed to the first reactor, 100, along with the output from the secondreactor, 400, which is the output stream, 410. The reactor 400 comprisespartially fluorinated 2-fluorochloropropanes plus additional HF, 330.Reactor 100 is the reactor for the first fluorination step. Reactor 100lacks a catalyst. This reactor may be a liquid phase reactor or a vaporphase reactor. The output of reactor 100, stream 110, may comprisepartially fluorinated 2-fluorochloropropanes, HCFC-235cb, HFC 236cb,hydrogen fluoride and hydrogen chloride and mixtures of two or morethereof.

Stream 110 proceeds to a separation column 200, wherein hydrogenchloride, 210, is removed as an overhead stream. Column 200 alsoreceives stream 610, which is the output stream from reactor 600 anddescribed more fully below. Bottom stream, 220, may comprise partiallyfluorinated chloropropanes, such as partially fluorinated HCFC-231 bb,HCFC-235cb, HCFC-236cb, hydrogen fluoride and mixtures of two or morethereof.

Stream 220 is then fed to a separation column, 300. The overhead steam,310, from column 300 may comprises partially fluorinated2-fluorochloropropanes, HCFC-235cb, HFC-236cb, hydrogen fluoride andmixtures of two or more. The bottom stream from column 300, stream 320,is then fed to second reactor, 400, along with additional hydrogenfluoride, 330. Stream 320 comprises chlorofluoropropanes and hydrogenfluoride. Reactor 400 is the reactor for the second fluorination stepand contains at least one catalyst.

The overhead stream from column 300, stream 310, which is fed toseparation column 500 to separate out the HFC-236cb/HFazeotrope/near-azeotropic if present as an overhead stream, 510, and apartially fluorinated 2-fluorochloropropanes/HF mixture and/or theHCFC-235cb/HF azeotrope/near-azeotrope mixtures comprise bottom stream,520. If HFC-236cb is not present, the overhead stream 510 comprises theHCFC-235cb/HF azeotrope/near-azeotrope mixture at the pressure at whichcolumn 500 is operated at. Bottom stream, 520, comprise partiallyfluorinated 2-fluorochloropropanes

The bottom stream, 520, is then fed to another second fluorination stepreactor, 600, which also has at least one catalyst which can be the sameor different from the catalyst in reactor 400, and along with additionalhydrogen fluoride, 530, to provide an output stream, 610, may comprisingHCFC-235cb, HFC 236cb, partially fluorinated 2-fluorochloropropanes,hydrogen fluoride and hydrogen chloride. Output stream, 610 is fed toseparation column 200.

Stream 510 can be separated further if desired, by using knownseparation techniques such as HF scrubbers or by using a multicolumnswing pressure distillation process.

FIG. 2 is a schematic illustrating a two column pressure swingdistillation process for separating3-chloro-1,1,1,2,2-pentafluoropropane (HCFC-235cb) or1,1,1,2,2,3-hexafluoropropane (HFC-236cb) from HF. In FIG. 2, stream 510(described above) is fed into a first distillation column 700 which isoperated at a first pressure and a first temperature; overhead stream710 is an azeotrope of the (HCFC-235cb) or (HFC-236cb) and HF,respectively, depending on the feed. The azeotrope compositions dependson the pressure at which the column 700 is operated. Overhead stream 710which feeds into a second distillation column 800, which is operated ata second pressure and a second temperature (which may be higher or lowerthan the first pressure and first temperature of column 700); outputstream 720 is the bottom stream from the distillation column 700, andcan be essentially pure HF, HCFC 235cb, or HFC 236cb depending on theoperating conditions of the column. Column 800 is a distillation columnwhich can be the same or different from column 700. Column 700 andColumn 800 are operated at different pressures. Stream 810 is theoverhead stream and is an azeotrope of the (HCFC-235cb) or (HFC-236cb)and HF, respectively, depending on the feed stream. Stream 820 is theoutput stream from the distillation column 800, and can be essentiallypure HF, HCFC 235cb, or HFC 236cb depending on the operating conditionsof the column. The distillation columns illustrated in FIGS. 1 and 2 canbe multistage and can have up to and including 20 theoretical stages.

As used herein, an azeotropic composition is a constant boiling liquidadmixture of two or more substances wherein the admixture distillswithout substantial composition change and behaves as a constant boilingcomposition. Constant boiling compositions, which are characterized asazeotropic, exhibit either a maximum or a minimum boiling point, ascompared with that of the non-azeotropic mixtures of the samesubstances. Azeotropic compositions as used herein include homogeneousazeotropes which are liquid admixtures of two or more substances thatbehave as a single substance, in that the vapor, produced by partialevaporation or distillation of the liquid, has the same composition asthe liquid. Azeotropic compositions as used herein also includeheterogeneous azeotropes where the liquid phase splits into two or moreliquid phases. In these embodiments, at the azeotropic point, the vaporphase is in equilibrium with two liquid phases and all three phases havedifferent compositions. If the two equilibrium liquid phases of aheterogeneous azeotrope are combined and the composition of the overallliquid phase calculated, this would be identical to the composition ofthe vapor phase.

For the purpose of this discussion, near-azeotropic composition means acomposition that behaves like an azeotrope (i.e., has constant boilingcharacteristics or a tendency not to fractionate upon boiling orevaporation). Thus, the composition of the vapor formed during boilingor evaporation is the same as or substantially the same as the originalliquid composition. Hence, during boiling or evaporation, the liquidcomposition, if it changes at all, changes only to a minimal ornegligible extent. This is to be contrasted with non-azeotropiccompositions in which during boiling or evaporation, the liquidcomposition changes to a substantial degree.

Near-azeotropic compositions exhibit dew point pressure and bubble pointpressure with virtually no pressure differential. That is to say thatthe difference in the dew point pressure and bubble point pressure at agiven temperature will be a small value, and in some near-azeotropecompositions the difference in dew point pressure and bubble pointpressure of less than or equal to 3 percent (based upon the bubble pointpressure).

It is also recognized that both the boiling point and the weightpercentages of each component of the azeotropic or near-azeotropicliquid composition may change when the azeotropic or near-azeotropicliquid composition is subjected to boiling at different pressures. Thus,an azeotropic or a near-azeotropic composition may be defined in termsof the unique relationship that exists among the components or in termsof the compositional ranges of the components or in terms of exactweight percentages of each component of the composition characterized bya fixed boiling point at a specified pressure. It is also recognized inthe art that various azeotropic compositions (including their boilingpoints at particular pressures) may be calculated (see, e.g., W. SchotteInd. Eng. Chem. Process Des. Dev. (1980) 19, 432-439). Experimentalidentification of azeotropic compositions involving the same componentsmay be used to confirm the accuracy of such calculations and/or tomodify the calculations at the same or other temperatures and pressures.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

Where applicants have defined an invention or a portion thereof with anopen-ended terms such as “comprising”, it should be readily understoodthat (unless otherwise stated) that the description includes the terms“consisting essentially of” and “consisting of”.

Also, use of “a” or “an” are employed to describe elements andcomponents described herein. This is done merely for convenience and togive a general sense of the scope of the invention. This descriptionshould be read to include one or at least one and the singular alsoincludes the plural unless it is obvious that it is meant otherwise.

Group numbers corresponding to columns within the Periodic Table of theelements use the “New Notation” convention as seen in the CRC Handbookof Chemistry and Physics, 81^(st) Edition (2000-2001).

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of embodiments of the disclosed invention, suitablemethods and materials are described below. All publications, patentapplications, patents, and other references mentioned herein areincorporated by reference in their entirety, unless a particular passageis cited. In case of conflict, the present specification, includingdefinitions, will control. In addition, the materials, methods, andexamples are illustrative only and not intended to be limiting.

EXAMPLES

The concepts described herein will be further described in the followingexamples, which do not limit the scope of the invention described in theclaims.

Example 1

Example 1 demonstrates the conversion of HCFC-231 bb into HCFC-235cb.

Into a 1 L Hastelloy C autoclave, 100 g of1,1,1,2,3-pentachloro-2-fluoropropane (HCFC-231 bb)(0.426 mole) and 256grams hydrogen fluoride (12.8 mole) is charged. The reactor is heated to130° C. After one hour, the reactor is cooled, and the contentstransferred to a second reactor having 10 g antimony pentafluoride. Thetemperature is raised to 120° C. while hydrogen fluoride is supplied atthe rate of 10 g per hour over a period of 3 hours. The reaction isconducted at this state for 20 hours while keeping the reactiontemperature at this level. The autoclave is cooled to −70° C., and HClpresent is vented. The remaining volatile products are collected byvacuum-line transfer into closed cylinder which is cooled to −70° C.while heating the autoclave. These volatiles are scrubbed in 20% aqueousHCl precooled to −60° C. and maintained near that temperature. The 48.0g of colorless oil collected after scrubbing and water washing is foundto contain 78% CF₃CF₂CH₂Cl (HCFC-235cb), 8% CF₃CF₂CH₂F (HFC-236cb), 8%CF₃CClFCH₂Cl (HCFC-234bb) and 4% CF₂ClCClFCH₂Cl (HCFC-233bb).

Example 2

Example 2 demonstrates phase studies of mixtures of HF and HFC-236cb.

A phase study was performed for a composition consisting essentially ofHFC-236cb and HF, wherein the composition was varied and the vaporpressures were measured at both 22.3° C. and 72.2° C. Based upon thedata from the phase studies, azeotrope compositions at other temperatureand pressures have been calculated.

Table 2 provides a compilation of experimental and calculated azeotropecompositions for HF and HFC-236cb at specified temperatures andpressures.

TABLE 2 Temperature, Pressure, Mole % Mole % ° C. psi HF HFC-236cb −6.115 55.1 44.9 11.2 30 52.5 47.5 22.6 45 50.9 49.1 31.3 60 49.8 50.2 38.475 48.9 51.1 40.7 105 47.6 52.4 42.6 150 46.1 53.9 72.6 195 45.0 55.083.3 255 43.9 56.1 91.9 315 43.1 56.9 102.0 405 41.7 58.3 108.0 490 36.963.1

Example 3

Example 3 demonstrates dew point and bubble point vapor pressures formixtures of HFC-236cb and HF.

The dew point and bubble point vapor pressures for compositionsdisclosed herein were calculated from measured and calculatedthermodynamic properties. The near-azeotrope range is indicated by theminimum and maximum concentration of HFC-236cb (mole percent, mol %) forwhich the difference in dew point and bubble point pressures is lessthan or equal to 3% (based upon bubble point pressure). The results aresummarized in Table 3.

TABLE 3 Azeotrope Near azeotrope compositions, Temperature, composition,mol % HFC-236cb ° C. mol % HFC-236cb Minimum Maximum −20 42.6 38.0 54.460 53.6 47.6 68.2 120 61.6 54.4 75.8

Example 4

Example 4 demonstrates phase studies of mixtures of HF and HCFC-235cb.

A phase study was performed for a composition consisting essentially ofHCFC-235cb and HF, wherein the composition was varied and the vaporpressures were measured at both 22.3° C. and 72.2° C. Based upon thedata from the phase studies, azeotrope compositions at other temperatureand pressures have been calculated.

Table 4 provides a compilation of experimental and calculated azeotropecompositions for HF and HCFC-235cb at specified temperatures andpressures.

TABLE 4 Temperature, Pressure, Mole % Mole % ° C. psi HF HCFC-235cb 8.315 82.7 17.3 26.4 30 79.6 20.4 38.2 45 77.7 22.3 47.1 60 76.2 23.8 54.475 75.1 24.9 66.1 105 73.3 26.7 79.3 150 71.4 28.6 89.5 195 70.1 29.9100.4 255 68.8 31.2 109.3 315 67.7 32.3 120.0 405 66.2 33.8 127.1 48065.1 34.9

Example 5

Example 5 demonstrates dew point and bubble point vapor pressures formixtures of HCFC-235cb and HF.

The dew point and bubble point vapor pressures for compositionsdisclosed herein were calculated from measured and calculatedthermodynamic properties. The near-azeotrope range is indicated by theminimum and maximum concentration of HCFC-235cb (mole percent, mol %)for which the difference in dew point and bubble point pressures is lessthan or equal to 3% (based upon bubble point pressure). The results aresummarized in Table 5.

TABLE 5 Azeotrope Near azeotrope compositions, Temperature, composition,mol % HCFC-235cb ° C. mol % HCFC-235cb Minimum Maximum −20 12.1 11.412.9 60 25.8 23.4 29.1 120 33.8 30.0 38.9

Example 6

Example 6 demonstrates azeotropic distillation for separation ofHFC-236cb from HFCF-235cb.

A mixture of HF, HFC-236cb and HCFC-235cb is fed to a distillationcolumn for the purpose of purification of the HFC-236cb. The data inTable 6 were obtained by calculation using measured and calculatedthermodynamic properties. The distillation column contains 30theoretical stages with the feed located 10 stages from the bottom. Thecolumn operates at 24.7 psia (10 psig) with a molar reflux ratio of 3.0.

TABLE 6 Compound or Column overhead variable Column feed (distillate)Column bottoms HCFC-235cb, 27.3 mol % 1 ppm (mole basis) 99.99 mol %HFC-236cb, 63.6 mol % 87.5 mol % 130 ppm HF,  9.1 mol % 12.5 mol % traceTemp, ° C. 0 7.2 43.4 Pressure, psia 44.7 24.7 25.3 (kPa)

Example 7

Example 7 demonstrates separation of HFC-236cb and HF via two columnpressure swing distillation.

A mixture of HF and HFC-236cb is fed to a distillation process for thepurpose of purification of the HF-236cb. The data in Table 7 wereobtained by calculation using measured and calculated thermodynamicproperties. The numbers at the top of the columns refer to FIG. 2.Referring to FIG. 2, the first column, 700, contains 15 theoreticalstages with the feed located 10 stages from the bottom. The columnoperates at 314.7 psia (300 psig) with a molar reflux ratio of 0.2. Thesecond column, 800, contains 17 theoretical stages with the feed located12 stages from the bottom. The column operates at 16.7 psia (2 psig)with a molar reflux ratio of 0.1.

TABLE 7 710 720 810 820 510 Column Column Column HFC- Compound Feed(700) 700 (800) 236cb or variable Mixture distillate Bottoms distillateproduct HF, 50 mol % 44.10 mol % 100.0 mol % 52..76 mol %  1 ppm (molebasis) HFC-236cb, 50 mol %  55.9 mol % 1 ppm 47.24 mol % 100 mol % (molebasis) Temp., ° C. −5.0 91.8 132.6 −3.5 2.4 Pres., psia (kPa) 64.7 314.7(2169.6) 314.8 (2170.4) 16.7 (115.1) 16.9 (116.5)

Example 8

Example 8 demonstrates separation of HCFC-235cb and HF via two columnpressure swing distillation.

A mixture of HF and HCFC-235cb is fed to a distillation process for thepurpose of purification of the HCFC-235cb. The data in Table 8 wereobtained by calculation using measured and calculated thermodynamicproperties. The numbers at the top of the columns refer to FIG. 2.Referring to FIG. 2, a 50/50 molar mixture of HF and HCFC-235cb is fedto a first distillation column (700) containing 12 theoretical stages.Column 700 operates with a top pressure of 16.7 psia (2 psig) and amolar reflux ratio of 0.1. Purified HCFC-235cb is recovered as thebottom stream from this first column. The second distillation column(800) contains 15 theoretical stages with the feed added to the 4thstage from the top of the column. Column 800 operates with a toppressure of 314.7 psia (300 psig) and a molar reflux ratio of 0.1.Purified HF is removed as the bottoms product from column 800.

TABLE 8 710 720 810 820 510 Column Column Column HCFC- Compound Feed(700) 700 (800) 235cb or variable Mixture distillate Bottoms distillateproduct HF 50.0 mol % 81.9 mol % 1 ppm 52.76 mol % 1 ppm (mole basis)(mole basis) HCFC-235cb 50.0 mol % 18.1 mol % 100.0 mol % 47.24 mol %100 mol % Temp., ° C. 25.0 10.6 31.6 −3.5 2.4 Pres., psia (kPa) 64.7(446) 16.7 (115) 16.8 (116) 314.7 (2170) 314.8 (2170)

Many aspects and embodiments have been described above and are merelyexemplary and not limiting. After reading this specification, skilledartisans appreciate that other aspects and embodiments are possiblewithout departing from the scope of the invention. Other features andbenefits of any one or more of the embodiments will be apparent from thefollowing detailed description, and from the claims.

And, not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed are not necessarily the order inwhich they are performed.

In the foregoing specification, the concepts have been described withreference to specific embodiments. However, one of ordinary skill in theart appreciates that various modifications and changes can be madewithout departing from the scope of the invention as set forth in theclaims below. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope ofinvention.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

It is to be appreciated that certain features are, for clarity,described herein in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures that are, for brevity, described in the context of a singleembodiment, may also be provided separately or in any subcombination.Further, reference to values stated in ranges include each and everyvalue within that range.

1. An azeotropic composition comprising about 44.9 mole percent to about63.1 mole percent 1,1,1,2,2,3-hexafluoropropane and about 36.9 molepercent to about 55.1 mole percent HF.
 2. The azeotropic composition ofclaim 1 wherein the composition has a boiling point between about −6.1°C. and 108° C. at a pressure from between about 15 psi and 490 psia. 3.A near-azeotropic composition comprising about 38 mole percent to about75.8 mole percent 1,1,1,2,2,3-hexafluoropropane and about 24.2 molepercent to about 62 mole percent HF.
 4. An azeotropic compositionconsisting essentially of about 44.9 mole percent to about 63.1 molepercent 1,1,1,2,2,3-hexafluoropropane and about 36.9 mole percent toabout 55.1 mole percent HF.
 5. The azeotropic composition of claim 4wherein the composition has a boiling point between about −6.1° C. and108° C. at a pressure from between about 15 psi and 490 psia.
 6. Anear-azeotropic composition consisting essentially of about 38 molepercent to about 75.8 mole percent 1,1,1,2,2,3-hexafluoropropane andabout 24.2 mole percent to about 62 mole percent HF.